1. Field of the Invention
The present invention relates to a substrate processing apparatus, and more particularly, to a substrate processing apparatus which forms a film on a semiconductor wafer utilizing plasma-excited processing gas.
2. Description of the Related Art
FIG. 10 is a schematic transverse sectional view for explaining a vertical type substrate processing furnace of a conventional substrate processing apparatus. A vertical sectional view taken along the line C-C in FIG. 10 corresponds to a vertical sectional view in FIG. 2. FIG. 11 is an enlarged vertical sectional view taken along the line C-C in FIG. 10.
Some substrate processing apparatuses which form a film on a semiconductor wafer utilizing plasma-excited processing gas have a structure that electrodes 269 and 270 for generating plasma are accommodated in electrode protecting tubes 275 in order to prevent a reaction with the processing gas.
Each of the electrode protecting tubes 275 is bent in the middle and a lower end inclined portion thereof projects outward from a side wall of a processing tube 203.
If a flexible member, e.g., a member having a knitted structure (braided structure) is used for the electrode 269 and the electrode 270, the electrodes 269 and 270 can be inserted into the electrode protecting tubes 275 from the lower end inclined portions of the electrode protecting tubes 275, and the electrodes 269 and 270 can reach upper ends of the electrode protecting tubes 275 (see a patent document 1).    Patent Document 1; Japanese Patent Application No. 2004-55446
If a knitted structure is employed for the flexible electrodes 269 and 270, the electrodes may become shorter than their original length because of their own weight and a decrease in elasticity due to the heat or long term use as shown in FIG. 12.
Moreover, as shown in FIG. 13, since the length is different from one individual to another because a member having a knitted structure is extensible, i.e. the member under tension increases in length, it is difficult to define the length.
The entire length may become shorter due to friction with the electrode protecting tube 275 as shown in FIG. 14.
Upper ends of the electrodes 269 and 270 are located higher than an uppermost wafer 200. If the length of the electrodes 269 and 270 is shortened, a plasma state (density and the like) at an upper portion in the furnace is different from a plasma state at the other portion. As a result, a thickness of a film formed on a wafer 200 located at the upper portion in the furnace is reduced, uniformity among the wafers is deteriorated, and a film forming result is deteriorated.